1. Field of the Invention
This invention relates to holography and more particularly to providing signals representative of information stored in a hologram.
2. Description of the Prior Art
The holographic art has been used for storing information in a multiplicity of applications, including a storage of a binary identification number on an identification card and a storage of an image on tape.
The identification card of the prior art typically has integral therewith a hologram which is a representation of a group of bits (ONE's and ZERO's) comprising the identification number. The genuineness of the card is verified by an apparatus which illuminates the hologram with a reconstructing beam of coherent light. In response to the reconstructing beam, a first order diffraction beam, representative of the group of bits, emanates from the hologram. The first order beam projects the representation of the group upon an array of detectors included in the apparatus.
The number of detectors in the array equals the number of bits in the group, each of the detectors providing a digital signal representative of a bit. In response to the projection of the group, the array provides a digital signal representation of the identification number. The verification apparatus additionally can include a data processing unit which compares the signal representation with signals representative of a multiplicity of issued numbers. When the identification number equals an issued number, the data processing unit generates an indication of the verification.
In a similar manner, the tape of the prior art has integral therewith a holographic recording of an image. In response to the reconstructing beam illuminating the holographic recording, a first order diffraction beam emanates therefrom whereby a representation of the image is projected upon a matrix of detectors. Typically, the matrix is comprised of 525 rows, each row including four hundred detectors (a 400 .times. 525 matrix). In response to the projection of the image, detectors of the matrix provide signals having amplitudes respectively representative of locations on the image. Typically, signals from the matrix are provided to a television signal processing unit.
It should be appreciated that because of the number of detectors in the array and the number of detectors in the matrix, both arrangements are costly. Additionally, the numbers of detectors cause the processing units to be costly.